Upon shutting down subterranean wells, stringent requirements are set with respect to barriers that are to prevent unwanted leakage of well fluids to the surroundings. A fluid-tight plug capable of withstanding continuous exposure to high pressure, high temperature, large forces and aggressive chemicals, must be set across the entire cross section of the well. Before being able to set the plug, different pipe bodies located in the well within the area where the plug is to be set, possibly may have been removed by virtue of mechanical cutting (so-called section milling). This process is very time-consuming, both due to the mechanical cutting and due to the subsequent removal of milled steel. It has proven difficult to ensure good adhesion and homogeneity of the plugging material, which usually is cement, both due to old, precipitated mud and due to remnants of milled steel pipes located in the well. The density and the stability of the plug may thus be impaired.
Patent publication WO 2012096580 describes a solution to this problem, and by virtue of pipe bodies in the well first being perforated using a perforation tool, for example a perforation gun. Then the well is flushed/purged by means of a washing tool before being plugged by means of a fluidized plugging material, for example hardening cement. Both with respect to the washing fluid and the fluidized plugging material, the perforations function as a passage between the inside and the outside of the pipe bodies.
Further, and in order to ensure a further improved density and homogeneity of the plug, patent publication WO 2012128644 describes an apparatus for improved displacement and distribution of the fluidized plugging material in the well.
In Norwegian patent application 20120277, a method and an apparatus for combined cleaning and plugging of a well is described. The method and apparatus are particularly suitable for use in wells provided with two or more substantially concentrically disposed pipe bodies in the longitudinal section to be plugged.